Electrolysis expansion performance of semigraphitic cathode in (K3AlF6/Na3AlF6)-AlF3-Al2O3 bath system

The electrolysis expansion of semigraphitic cathode in [K3AlF6/Na3AlF6]-AlF3-Al2O3 bath system was tested by self-made modified Rapoport apparatus. A mathematical model was introduced to discuss the effects of αCR (cryolite ratio) and βKR (elpasolite content divided by the total amount of elpasolite and sodium cryolite) on performance of cathode electrolysis expansion. The results show that K and Na (potassium and sodium) penetrate into the cathode together and have an obvious influence on the performance of cathode electrolysis expansion. The electrolysis expansion and K/Na penetration rate increase with the increase of αCR. When αCR=1.9 and βKR=0.5, the electrolysis expansion is the highest, which is 3.95%; and when αCR=1.4 and βKR=0.1, the electrolysis expansion is the lowest, which is 1.28%. But the effect of βKR is correlative with αCR. When αCR=1.6 and 1.9, with the increase of βKR, the electrolysis expansion and K/Na penetration rate increase. However, when αCR=1.4, the electrolysis expansion and K/Na penetration rate firstly increase and then decrease with the increase of βKR.